Application of Fluids to Substrates

ABSTRACT

Various embodiments relate to application of a fluid to a substrate. The fluid is locally heated, for example, to obtain a desired thickness profile.

This is a divisional application of U.S. application Ser. No.13/891,644, entitled “Application of Fluids to Substrates” which wasfiled on May 10, 2013 and is incorporated herein by reference.

TECHNICAL FIELD

The present application relates to apparatuses, methods and techniquesrelated to the application of fluids to substrates.

BACKGROUND

In various industrial applications a fluid is applied to a substrate.One example from the semiconductor industry is the application of glueto a semiconductor wafer, for example, a silicon wafer, for mounting thesame to a carrier like a glass carrier prior to carrying out a thinningprocess like a grinding or etching process.

In such processes, a thinning of the wafer has to be performed asuniform as possible, i.e., a total thickness variation (TTV) of thewafer after the thinning is kept at a minimum, for example, within alimit of ±3 μm. An uneven application of the glue may contribute to thetotal thickness variation.

Other fluids which may be applied to substrates in industrial processesinclude imides, lacquers or photoresists. Also, in such cases, a uniformapplication of the fluid on the substrate, for example, with a thicknessvariation within desired limits, may be desirable.

BRIEF DESCRIPTION OF THE DRAWINGS

Illustrative embodiments will be described with reference to theattached drawings, wherein:

FIG. 1 schematically shows an example for an application wheretechniques, apparatuses, methods etc. according to embodiments may beapplied;

FIG. 2 schematically illustrates a fluid application apparatus accordingto an embodiment;

FIG. 3, which includes FIGS. 3A and 3B, shows example measurementresults for illustrating some features of some embodiments;

FIG. 4 illustrates a method according to an embodiment; and

FIG. 5 illustrates a server method according to an embodiment.

In the following, embodiments will be described with reference to theattached drawings. These embodiments serve only as implementationexamples and are not to be construed as limiting. For example, otherembodiments may include less features, more features, alternativefeatures etc. compared to the embodiments described and shown in thedrawings. Moreover, features from different embodiments may be combinedwith each other unless noted otherwise to form further embodiments.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Embodiments described below relate to the application of a fluid to asubstrate, i.e., a fluid having a viscosity which, as explained below,may be temperature-dependent. The fluid will also be referred to asviscous fluid in some embodiments, to indicate that the viscosity may bemodified in such embodiments. This, however, does not imply any specificvalue of the viscosity of the fluid. Generally, the viscosity of a fluidis a measure of resistance to gradual deformation by shear stress ortensile stress and is heat-dependent. In various embodiments, by locallyheating the fluid on the substrate, for example, by locally heating thesubstrate adjacent to the fluid, the viscosity of the fluid may belocally changed. In some embodiments, this may be used to locally adjustthe thickness of the fluid on the substrate. Suitable fluids include,for example, glues, lacquers, imides, photoresists and the like. In oneor more embodiments, a thickness variation of the fluid over thesubstrate may be reduced by local heating. In alternative embodiments,to obtain a suitable heating pattern or heating scheme a calibration maybe used.

Turning now to the figures, in FIG. 1 an exemplary scenario wheretechniques, methods, apparatuses etc. discussed in the following withreference to FIGS. 2-5 may be employed. It should be noted that theapplication of these techniques, apparatuses and methods, however, isnot limited to the scenario shown in FIG. 1, but may be applied in anysituation where a viscous fluid is applied to a substrate.

In particular, FIG. 1 shows three stages (a), (b) and (c) of a thinningprocess of a semiconductor wafer 10, for example, a silicon wafer.Semiconductor wafer 10 is an example for a substrate usable inembodiments. Other substrates may, for example, include glasssubstrates.

In stage (a), substrate 10 is mounted to a carrier 11, for example, asolid carrier made of glass, metal, plastic or any other suitablematerial. To mount substrate 10 to carrier 11, a glue 12 is providedbetween substrate 10 and carrier 11. In the example shown, the glue isstructured to form strips. In other embodiments, glue 12 may coveressentially the whole area (with a possible exception of a peripheralarea) between substrate 10 and carrier 11.

In stage (b), substrate 10 mounted to carrier 11 is grinded by agrinding wheel 13 moving about the surface of substrate 10. In theexample shown, an outer peripheral region 14 of substrate 10 is notgrinded, thus leaving a thicker ring at the periphery of substrate 10while the center region is thinned.

In stage (c), an etching is performed. To achieve this, substrate 10together with carrier 11 are placed on a chuck 15 and are suspendedwithin a ring 17 or within individual pins 17 on a gas cushion, forexample, an air cushion. Gas for the gas cushion may be supplied via achannel 16. Chuck 15 may be rotatable or stationary. Etchant 110 issupplied via a nozzle 18, which nozzle 18 may be movable as indicated byan arrow 19 to perform a desired etching.

For some applications, high requirements regarding the total thicknessvariation of substrate 10 after the etching of stage (c) (possibly withthe exception of peripheral region 14) may exist. For example, someapplications may demand that a total thickness variation is ±3 μm orbelow. Each of the three stages (a), (b) and (c) may contribute to thefinal total thickness variation. For example, variations in thickness ofglue 12 may cause the total thickness variation to increase. In someembodiments, for applying glue 12, techniques, apparatuses or methodsdescribed in the following with respect to FIGS. 2-5 may be used, whichmay help to reduce a thickness variation of glue 12 in some cases andtherefore may contribute to a reduced total thickness variation.

In FIG. 2, an apparatus is shown which is usable to apply a viscousfluid 22 to a substrate 23. In some embodiments, fluid 22 may be a glue,for example, glue 12 of FIG. 1. However, other viscous fluids may alsobe applied using the apparatus of FIG. 2, for example, imides, lacquers,photoresists and the like. In embodiments, fluid 22 has atemperature-dependent viscosity. For example, a viscosity of fluid 22may be decreased when the fluid is heated.

In some embodiments, substrate 23 may be a semiconductor wafer likesubstrate 10 of FIG. 1. In other embodiments, still other substrates maybe used. For example, substrate 23 may be a carrier like a glass carrierusable to receive a further substrate like a semiconductor wafer.

Substrate 23 is provided on a chuck 24 which is rotatable as indicatedby an arrow 25. Rotation of chuck 24 may be controlled by a controller28. Instead of chuck 24, in other embodiments, a different kind ofholder for substrate 23 may be used. For example, in some embodiments anon-rotating holder may be used, and fluid application device 22 maymove across the surface of substrate 23 to apply fluid 22. By locallyheating fluid 22 to change its viscosity, the thickness profile may thenchange under the influence of gravity.

To apply fluid 22 to substrate 23, a fluid application device 20 (forexample, comprising a nozzle) applies fluid 22 to substrate 23, forexample, at or near a center of substrate 23, and by rotating chuck 24and therefore substrate 23, fluid 22 is dispersed over substrate 23. Incase of a high viscosity of fluid 22, this dispersion may lead to acomparatively uneven distribution of fluid 22, which may be undesirable.

In the apparatus of FIG. 2, a heating mechanism is provided to locallyheat fluid 22. Such a local heating may, for example, be performed bylocally heating substrate 23. Fluid 22 may then thermalize locally tothe corresponding temperature of substrate 23, for example, in caseswhere a comparatively thin layer of fluid 22 is provided on substrate23. In other embodiments, fluid 22 may be locally heated directly. Insome embodiments, by locally heating fluid 22 a viscosity of fluid 22may be modified, for example, lowered. For example, the fluid at ambienttemperature, for example, room temperature, may be a highly viscousfluid showing non-Newtonian properties.

Generally, the behavior of a Newtonian fluid may be described by thelaws of Navier-Stokes. A Newtonian fluid may have tensors that describethe viscous stress and strain rate which are related by a constantviscosity tensor that is independent of stress state and velocity of theflow. Non-Newtonian fluids differ from such a behavior. By locallyheating the fluid, the viscosity of the fluid may be lowered, so it moreclosely resembles properties of a Newtonian fluid. Movement of Newtonianfluids is well understood and can be controlled more easily than themovement of non-Newtonian fluids. As mentioned above, Newtonian fluidsfollow the laws of Navier-Stokes. Even if the fluid is not strictlyNewtonian, through heating the properties may resemble Newtonianproperties more, which in some embodiments may make control of thebehavior of fluid 22, for example, control of its thickness acrosssubstrate 23, easier.

In the apparatus of FIG. 2, as a heating mechanism an infrared lightsource 21 is provided which is movable as indicated by arrows 27 tolocally heat substrate 23 and fluid 22 dispersed thereon. Controller 28may control movement and/or intensity of infrared lamp 21. In otherembodiments, controller 28 may control the operation of a differentheating mechanism. In some embodiments, controller 28 may be implementedby programming a microprocessor-based device like a computeraccordingly. In other embodiments, an infrared lamp comprising aplurality of segments and covering essentially a whole radius ofsubstrate 23 from center to periphery may be provided, and localheating, in this case heating at a desired distance from the center ofsubstrate 23, may be achieved by activating corresponding segments ofthe infrared lamp. Through rotation of substrate 23, together with chuck24, then a radially symmetric heating profile may be obtained in someembodiments. In other embodiments, other heating mechanisms may beprovided, for example, a resistive heating (electrical heating) providedin chuck 24 to heat substrate 23 and therefore fluid dispersed on thesubstrate.

Furthermore, in the apparatus of FIG. 2 an optional fluid thicknessmeasurement device 26 is provided. Using fluid thickness measurementdevice 26, a thickness of the fluid 22 on substrate 23 may be measured,for example, via optical means like ellipsometry or other reflectivetechniques, or via tactile techniques or ultrasonic techniques.Generally, any conventional technique may be used for layer thicknessmeasurement. In some embodiments, to obtain a desired thickness profileof fluid 22 on substrate 23, fluid 22 is applied to substrate 23 and thethickness across the substrate is measured by device 26.

When there are deviations from a desired thickness profile a localheating via infrared lamp 21 may be performed. In some embodiments, sucha local heating may be performed at locations where a thickness of fluid22 on substrate 23 is greater than a desired thickness. This process,i.e., measuring the thickness and applying or adjusting local heating,may be repeated until a desired thickness profile is reached. In someembodiments, a pattern or scheme of heating (for example, positions ofinfrared lamp 21, duration and intensity of heating etc.), or segmentswhich are activated in case of a segmented heating, current in case of aresistive heating etc., during this process may be stored and usedlater, for example, during a production process to apply fluid tosubstrates with a desired thickness profile.

A calibration as described above, i.e., determining and storing apattern or scheme of heating, may be repeated, for example, in regularintervals like once a week, after a predetermined quantity of substratesprocessed or after control measurements indicate that a desiredthickness profile, for example, a profile which is flat within a certaintolerance, is not obtained any longer.

FIG. 3 shows measurement results to illustrate the effect of localheating.

In FIG. 3(a), glue has been applied to a substrate 30. A glue thicknessin an area labeled 31 was generally lower than a glue thickness in anarea labeled 32. The thickness differences were of the order of a fewmicrometers.

Following this, local heating at the center of substrate 30 was appliedwhile rotating the substrate, which is symbolized by an arrow 35. Theresult is shown in FIG. 3(b). Here, the thickness of the glue at thecenter 33 is lowest, while the thickness is highest at a peripheralregion 34. The thickness differences in this case were some tenmicrometers. This shows that by local heating, the thicknessdistribution of a viscous fluid like a glue may be influenced. Forexample, by adjusting the intensity of the heating the effect may befine-tuned to the needs of a specific application.

In FIGS. 4 and 5, flowcharts illustrating methods according to someembodiments are depicted. While the methods are illustrated as a seriesof acts or events, it should be noted that embodiments are not limitedto the order of these acts or events shown. In other embodiments, adifferent order may be used, or some of the acts or events shown may beperformed concurrently with each other. For example, in someembodiments, an application of a viscous fluid to a substrate and arotating of the substrate are shown in separate boxes one after theother, although these acts may also be performed concurrently with eachother, or a rotation may start prior to the application of the fluid.

In FIG. 4, a method for calibration of a local heating of a fluid beingapplied to a substrate is shown. The method of FIG. 4 may, for example,be implemented using the apparatus of FIG. 2, but may also be used usingother apparatuses or devices which enable a local heating of a fluidapplied to a substrate.

At 40, a viscous fluid is applied to a substrate. The viscous fluid may,for example, comprise a glue, an imide, a lacquer or a photoresist. Theviscous fluid may have a temperature-dependent viscosity. In someembodiments, the viscous fluid may exhibit a non-Newtonian behavior atambient temperature, e.g., room temperature.

In some embodiments, the substrate may be a semiconductor wafer like asilicon wafer. In other embodiments, other kinds of substrates, forexample, glass substrates, or carriers to receive further substrates,may be used.

At 41, the substrate is rotated, which is also sometimes referred to asspinning, to disperse the substrate on the wafer. In other embodiments,the fluid may be dispersed by other methods than spinning, for example,by moving a fluid application device across the surface of thesubstrate.

At 42, a fluid thickness on the substrate is measured.

At 43, it is checked if the measured fluid thickness corresponds to adesired thickness profile. For example, it is checked if the thicknessvariation of the fluid is within a desired tolerance, for example, ±1μm, ±3 μm or ±5 μm. However, other desired thickness profiles than aflat profile with a thickness variation within a tolerance may also beused in embodiments.

If the thickness profile corresponds to a desired profile, the method isended at 45. Otherwise, a local heating of the fluid on the substrate isadjusted at 44. For example, portions where a thickness exceeds adesired thickness or a mean thickness by more than a desired amount maybe locally heated, e.g., by some degrees centigrade to increase aviscosity of the fluid at these locations. Adjusting of a local heatingmay, for example, comprise moving an infrared lamp to desired locations,activating desired lamp segments, activating resistive heating elements,adjusting a power of infrared lamps or a magnitude of a heating currentetc.

After that, the method goes back to 41 and is repeated until at 43 thethickness profile corresponds to a desired behavior. The heating patternor scheme obtained by various adjustments at 44 may be stored to be usedlater during production, for example, during the method illustrated inFIG. 5 to be described later.

In FIG. 5, a flowchart illustrating a method according to a furtherembodiment is shown. At 50, a viscous fluid is applied to a substrate.The viscous fluid may, for example, comprise a glue, an imide, lacquer,a photoresist or the like. In embodiments, the viscous fluid may have atemperature-dependent viscosity. In some embodiments, at ambienttemperature the viscous fluid may exhibit a non-Newtonian behavior. Insome embodiments, the substrate may comprise a semiconductor wafer likea silicon wafer. In other embodiments, the substrate may be a differenttype of substrate, for example, a glass substrate.

At 51, the substrate is rotated to disperse the fluid on the substrate.In other embodiments, other techniques may be used to disperse the fluidon the substrate.

At 52, a predetermined local heating is applied to the fluid. In someembodiments, the predetermined local heating may have been determined bya calibration process, for example, the method as explained withreference to FIG. 4. In other cases, the predetermined local heating maybe preset for specific substrate types and/or fluid types. In someembodiments, the predetermined local heating may be applied while thesubstrate is rotating. In some embodiments, by applying thepredetermined local heating a thickness variation of the fluid on thesubstrate is reduced, for example, reduced below a desired tolerance.

Optionally, at 53 further processing may be performed. For example, theprocessing illustrated with respect to FIG. 1 may be performed in casethe fluid is a glue, i.e., the substrate may be mounted to a carrier,and a grinding and/or etching may be performed. For other kinds offluids, other kinds of processing may be performed. For example, in casethe fluid is a photoresist, a photolithography may be performed.

As can be seen from the above description of modifications andalterations, the embodiments shown serve only illustrative purposes andare not to be construed as limiting the scope of the present applicationin any way. In particular, the techniques, concepts and schemesdescribed herein may be implemented in a manner different from themanners shown.

What is claimed is:
 1. An apparatus comprising: a substrate holder; afluid application device configured to apply a fluid to a substrate onthe substrate holder; a heating mechanism configured to locally heat thefluid; and a controller configured to control the heating mechanism toapply a local heating in order to obtain a desired thickness profile ofthe fluid on the substrate.
 2. The apparatus of claim 1, wherein thefluid comprises at least one of a glue, an imide, a lacquer, and aphotoresist.
 3. The apparatus of claim 1, wherein a viscosity of thefluid is temperature-dependent.
 4. The apparatus of claim 1, wherein theheating mechanism comprises an infrared lamp.
 5. The apparatus of claim1, wherein the substrate holder is rotatable.
 6. The apparatus of claim5, wherein the fluid application device is configured to apply the fluidwhile the substrate holder rotates.
 7. The apparatus of claim 5, whereinthe controller is configured to control the heating mechanism to locallyheat the fluid while the substrate holder rotates.
 8. The apparatus ofclaim 1, further comprising a fluid thickness measurement device, theapparatus being further configured to determine a local heating patternthrough a calibration measurement using the fluid thickness measurementdevice.
 9. The apparatus of claim 1, wherein the substrate holder isconfigured to receive semiconductor substrates.
 10. The apparatus ofclaim 1, wherein the local heating locally changes a behavior of thefluid from an essentially non-Newtonian behavior to an essentiallyNewtonian behavior.